Former U.S. Vice President Joe Biden has expanded his lead over a wide field of candidates for the 2020 Democratic presidential nomination by 5 percentage points since he entered the race in late April, according to a monthly Reuters/Ipsos poll.

The poll released Wednesday found 29% of Democrats and independents said they would vote for Biden in the state nominating contests that begin next year. That is up from 24% who said so in a poll that ran in late April, days before Biden announced his bid.

Biden led the field among all major demographic groups except millennials (ages 18-37), who favored U.S. Senator Bernie Sanders of Vermont over Biden 18% to 16%.

Biden, 76, remains in the strongest position for the top of the ticket despite questions about his age and centrist positions. He also has faced criticism over his unwanted touching of women and his treatment of law professor Anita Hill three decades ago during Supreme Court Justice Clarence Thomas' confirmation hearing.

FILE - Democratic presidential candidate U.S. Sen. Bernie Sanders (I-VT) speaks at a news conference to introduce the Medicare for All Act of 2019 on Capitol Hill in Washington, April 10, 2019.

The monthly survey showed 29% of women who identify as Democrats and independents said they backed Biden, up 4 points from last month.

And among registered Democrats, those who supported other candidates still listed Biden as a top alternative if their choice dropped out of the race, according to the poll.

"That means that there is not a significant anti-Biden block of voters split between the other candidates," said Chris Jackson, a polling expert at Ipsos.

"At this moment, Joe Biden is a clear front-runner in the Democratic primary," Jackson added.

The Democratic nominee will likely face Republican President Donald Trump in the November 2020 election.

Sanders next

Besides Biden, 13% of Democrats and independents said they would vote for Sanders. None of the other candidates received more than 6% support in the poll.

With more than a month until the candidates square off in the first televised debates and 18 months before the 2020 presidential election, the American public appears to be selecting candidates they know best.

Less than 20% of Democrats said they were familiar with many of the candidates, including U.S. Representative Tulsi Gabbard of Hawaii, former Colorado Governor John Hickenlooper, Montana Governor Steve Bullock, Washington Governor Jay Inslee and Wayne Messam, mayor of Miramar, Florida. In comparison, more than 84% said they were familiar with Biden and Sanders.

However, Biden probably is not leading on name recognition alone, said Kyle Kondik, a political analyst at the University of Virginia Center for Politics.

"It's not valuable if people know you but don't like you," Kondik said. "We saw that for [former Florida Governor] Jeb Bush in 2015. He had good name ID — everyone knew his family name — but he wasn't polling as well as Biden is now because Republicans didn't like him."

Poll details

The Reuters/Ipsos poll was conducted online in English throughout the United States on May 10 and 13. It gathered responses from 1,132 Democrats and independents and has a credibility interval, a measure of precision, of 3 percentage points.

Respondents were asked to pick from 23 potential Democratic nominees, including New York City Mayor Bill de Blasio, who is expected to announce his plans this week. The poll did not include 89-year-old Mike Gravel, a former U.S. senator from Alaska, who is running.